The normal term of a human pregnancy is in the range of 37 to 42 weeks with 40 weeks being typical. Infants born more than 3 weeks before full term (i.e. at less than 37 weeks of gestation) are called ‘premature’.
Approximately one of every eight infants born in the United States is premature. Premature infants tend to be underweight in comparison to full term infants. Premature infants also tend to suffer from various health problems. These health problems can be very complicated. Such health problems may stem from the fact that a premature baby's organs may not yet have developed to the point that the baby can live independently outside of the womb. For example, premature infants often have difficulty breathing and regulating their body temperatures and may have other problems caused by underdevelopment of a range of organs. These problems particularly affect infants born before 35 weeks gestational age. All biological systems in such infants are immature having been previously regulated through the mother's placenta.
Critical biological systems that can be underdeveloped in premature infants include:                the central nervous system (e.g. brain)        the cardiovascular system,        the immune system and        the gastro-intestinal system.        
The health problems faced by premature infants tend to vary depending upon how prematurely the infants are born. Infants born in the later preterm (i.e. between 35 and 37 weeks gestation) may look like full term babies. However, even late preterm babies tend to be at greater risk for certain health problems than full term babies.
Infants born at or before 34 weeks of gestation typically lack the ability to suck and swallow in a coordinated manner.
Infants born between 32 and 34 weeks of gestation may be called ‘moderately preterm’. Infants born at less than 32 weeks of gestation may be called ‘very preterm’. Infants born at or before 28 weeks of gestation may be called ‘extremely preterm’.
Infants weighing less than 1500 grams and/or being eight weeks or more premature (i.e. very or extremely premature infants having gestation of 32 weeks or less), can be exceedingly frail and usually require support to stay alive and grow. With their immature biological systems, these infants cannot breathe on their own to maintain normal oxygen levels, regulate their body temperatures, fight infections effectively or feed adequately.
Premature infants are typically held in a neonatal intensive care unit (NICU) where their health may be carefully monitored. Monitoring premature infants often includes blood tests (e.g. to check glucose, oxygen, and bilirubin levels); chest X-rays, and continuous cardiorespiratory monitoring.
Premature infants are often placed in incubators or “isolettes” in which air temperature is controlled. Many incubators also include systems for controlling humidity of the air inside the incubator. Some incubators also include facilities for controlling oxygen content of the air inside the incubator.
An incubator in a NICU may, for example, provide:                delivery of ambient oxygen to help maintain oxygen levels;        a relatively closed volume to exclude environmental dust/pollutants which can cause lung damage;        systems for controlling temperature to help maintain body temperature;        systems for maintaining and controlling humidity to prevent skin breakdown which is linked to increased risk of infection;        a relatively sterile space to help prevent infection; and/or        attenuation of some ambient light and noise to allow the infant to rest.        
It is challenging to assess whether premature infants are experiencing pain or stress because they may not respond to pain in the ways typical of full-term infants. Some caregivers may take the lack of ‘normal’ response to painful stimuli to indicate that premature infants are not bothered by pain. The inventors consider that this is a particular problem that is made worse by the fact that premature infants are subjected to frequent procedures that can be painful such as heel pricks to obtain blood for testing. Such painful stimuli cause stress to premature infants. While such stress can adversely affect the infants, the procedures are necessary and it is not generally practical to control this type of pain in premature infants using analgesic drugs. The inventors believe that methods and apparatus that may be used to reduce stress in premature infants may improve health outcomes for those infants.
There remains a need for effective techniques for improving health outcomes for premature infants, especially ‘very’ and ‘extremely’ premature infants.